1. Place potatoes in a large pot and cover with water. Bring to a boil, then reduce heat and simmer until tender, about 15-20 minutes. Drain and let cool.
2. In a large mixing bowl, combine mayonnaise, dijon mustard, celery, red onion, apple cider vinegar, salt, and black pepper.
3. Add the cooled potatoes to the bowl and gently mix until well coated.
4. Garnish with chopped fresh parsley before serving.